[alsa-devel] [PATCH RFC v2 REPOST 3/8] ASoC: davinci-evm: HDMI audio support for TDA998x trough McASP I2S bus
jsarha at ti.com
Wed Jan 15 17:28:14 CET 2014
On 01/15/2014 03:48 PM, Anssi Hannula wrote:
> 15.01.2014 13:27, Jyri Sarha kirjoitti:
>> On 12/31/2013 03:25 PM, Mark Brown wrote:
>>> On Fri, Dec 20, 2013 at 12:39:38PM +0200, Jyri Sarha wrote:
>>>> support. The only supported sample format is SNDRV_PCM_FORMAT_S32_LE.
>>>> The 8 least significant bits are ignored.
>>> Where does this constraint come from?
>> From driver/gpu/drm/i2c/tda998x_drv.c. The driver configures CTS_N
>> register statically to a value that works only with 4 byte samples.
>> According to my tests it is possible to support 3 and 2 byte samples too
>> by changing the CTS_N register value, but I am not sure if the
>> configuration can be changed on the fly. My data sheet of the nxp chip
>> is very vague about the register definitions, but I suppose the register
>> configures some clock divider on the chip. HDMI supports only upto 24bit
>> audio and the data sheet states that any extraneous least significant
>> bits are ignored.
> That sounds strange, CTS/N values only depend on audio sample rate and
> TMDS/video clock, not on the audio format or the size of samples (HDMI
> spec sec 7.2 - Audio Sample Clock Capture and Regeneration).
> Sure there isn't anything more going on (like the used HDMI sink being
> more tolerant to wrong CTS/N with 4-byte samples, or more likely
> something else I can't immediately think of)?
On theoretical level I am not really sure about anything, because have
not been able to get my hands on proper NXP TDA19988 documentation.
However, while playing around with my Beaglebone-Black I have have found
out in practice that by changing CTS_N register's (page 0x11 reg 0x0c)
K_SEL bits (bit 2 to 0) I can get 2, 3 and 4 byte samples to work
consistently by setting:
K_SEL = 1 for SNDRV_PCM_FORMAT_S16_LE
K_SEL = 2 for SNDRV_PCM_FORMAT_S24_3LE
K_SEL = 3 for SNDRV_PCM_FORMAT_S32_LE
Because I do not really know what is going on, I did not want to suggest
any changes to the driver and just use the format that works with the
current driver version.
The HDMI sinks I have been using are a Toshiba 22B2LF1G and Thomson
42E90NF32 televisions. About those I just know that they both behave the
 The closest data sheet that has any description about the chip
registers I have found is this:
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